This invention relates to a thread tension control device of sewing machine which is automatically operated to control the thread tension in accordance with the stitching types of the sewing machine.
The most suited stitches or seams can be obtained only by suitably controlling the upper thread tension in accordance with the conditions in dependence upon the stitching types. However there have not been offerred any proposals which are to automatically control the upper thread tension in response to various stitching conditions, and therefore desired or suitable formation of stitches have been obtained only by manual adjustment of the thread tension device in accordance to the stitching conditions.
This invention has been devised to eliminate such a disadvantage of the prior art.